if someone has a lot of glass for a manual SLR system you can get a thing called a "speed booster" for most common mounts , it has optics in it to convert the image area and the back focus distance to give you the frame the lens had originally. (mostly within about 5% or so)
I've got a mid range china brand one and it works quite well.
Stu
I've got a mid range china brand one and it works quite well.
Stu